Heat sink and transistor retaining assembly

ABSTRACT

A heat sink and transistor retaining assembly for installation onto a printed circuit board. The assembly has a thermally conductive base plate forming a heat sink adapted to be disposed adjacent to the board, a first electric insulator attached to the base plate, a plurality of transistors positioned at predetermined positions against the first electric insulator so as to be electrically insulated from the base plate, a second electric insulator adjacent to the transistors with the transistors sandwiched between the insulators, and a resilient clamp attached to the base plate with the electric insulators and transistors positioned therebetween. The clamp has a plurality of retaining fingers that exert a retaining force on the transistors between the first and second insulators to retain the transistors in predetermined positions relative to the board. The assembly is secured together as a unit after its several components have been positioned in a fixture that supports and retains the component in predetermined positions.

TECHNICAL FIELD

The present invention relates transistor to heat sinks, and moreparticularly, to heat sinks for a plurality of transistors mounted ontoa printed circuit board of an electronic device.

BACKGROUND OF THE INVENTION

When electricity is passed through transistors mounted on a printedcircuit board (hereinafter "the board"), the transistors, particularlypower transistors, generate a substantial amount of heat. The heat mustbe drawn away from the transistors and dissipated to maintain lowtemperatures and to avoid damaging the transistors. Conventionaltransistor heat sinks are mounted on the cases of the transistors sinkafter electrical leads of the transistors have been inserted andsoldered onto the board. However, the transistor case is often drawnagainst the heat sink when a mounting screw is tightened, so theelectric leads have to bend. As a result, stress from bending forces isexerted on the leads and on solder joints that join the leads to theboard, wherein the stress can lead to breakage or failure of thetransistor.

A second conventional heat sink and transistor assembly includes a heatsink in the form of a cap structure having cooling fins that attach toand fit over one or more transistors. The cap structure is installedafter the transistors are soldered to the board, so stress from bendingand compression forces is exerted on the leads and solder joints duringinstallation.

Strict manufacturing standards for, as an example, electronic medicaldevices, require that the case of a transistor have sufficient clearanceover the surface of the board, and be spaced apart from othercomponents. Conventional assemblies have experienced significantdifficulties maintaining correct positioning of the transistors whenthey are attached to the board before being secured to a heat sink.

Regardless of which type of conventional heat sink is used, it isnecessary to insert and then solder each transistor individually ontothe printed circuit board. It is then necessary to perform the oftenlaborious task of fastening one or more heat sinks to the transistor. Asa result, manufacturing processes used during installation of thetransistors onto the board are very labor intensive, time-consuming, andhave a high risk of improper transistor positioning and excessive leadstress, thereby requiring costly rework of the assemblies.

Accordingly, there is a need for an assembly that permits heat sinks tobe mounted on transistors and the transistors to be installed on aprinted circuit board in a quick and inexpensive manner and in theproper positioning without stressing the transistor leads.

SUMMARY OF THE INVENTION

The present invention provides a heat sink and transistor retainingassembly mountable to a printed circuit board that retains, supports,and properly positions a plurality of transistors in known positionswhile minimizing stresses on transistor leads when the assembly ismounted onto the board. A preferred embodiment of the present inventionhas a thermally conductive base plate forming a heat sink, a pluralityof transistors positioned and sandwiched between two electric insulatorsthat are fastened to the heat sink, and a resilient clamp attached tothe heat sink with the first and second electric insulators sandwichedtherebetween. As such, the transistors are secured in the predeterminedpositions and adapted to be installed and electrically connected to theboard as a unit. The clamp mounts onto the board with mounting legs thatsupport the assembly perpendicular to the board. The clamp has aplurality of retaining fingers that exert a retaining force on each ofthe transistors to secure them between the electric insulators above theboard.

The heat sink and transistor retaining assembly of the preferredembodiment is assembled using a fixture having a base with a datumsurface representing the board and a plurality of apertures adapted toreceive the transistor leads. A plurality of support pegs extend upwardfrom the datum surface and are adapted to support the transistors at thepredetermined positions over the datum surface and in a desired properalignment. Each peg is positioned adjacent to at least one other supportpeg with two or more lead apertures between the two support pegs. Thefixture further includes alignment guides to align the heat sink, theelectric insulators, and the clamp in a consistent position, so theassembly can be manufactured by placing the assembly's individualcomponents onto the fixture, fastening the components together andremoving the assembly as a unit from the fixture, wherein the unit isready to be mounted onto the board.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top isometric view of two heat sink and transistor retainingassemblies, in accordance with the present invention, mounted on sidesof a printed circuit board of an electronic device.

FIG. 2 is an enlarged, exploded top isometric view of one of the heatsink and transistor retaining assemblies of FIG. 1 having seventransistors, with the board being partially cut away.

FIG. 3 is an enlarged, exploded top isometric view of the second heatsink and transistor retaining assembly of FIG. 1 having four transistorsremoved from the board.

FIG. 4 is a reduced, top isometric view of the heat sink and transistorretaining assembly of FIG. 3 positioned over a fixture, in accordancewith the present invention, that is used to assemble the heat sink andtransistor retaining assembly.

FIG. 5 is an enlarged, partially cut away top isometric view of analternate embodiment of the heat sink and transistor retaining assemblyof FIG. 4 having a heat sink with two fins.

FIG. 6 is a cross-sectional view taken substantially along line 6--6 ofFIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1, a heat sink and transistor retaining assembly 10, inaccordance with the present invention, has a plurality of transistors 12positioned adjacent to a heat sink 18 and secured in place with asupporting clamp 20. The transistors 12 have leads 22 that extenddownward below the heat sink 18 and are adapted to engage a printedcircuit board 24. The assembly 10 attaches to the board 24 with theleads 22 in electrical contact with the board, which is mountable in,for example, a medical electronic device or the like. The assembly 10 issupported on the board 24 by mounting legs 26 on the clamp 20 that mountto the board so the transistors 12 are retained and supported atpredetermined positions above the board with adequate spacing betweenadjacent transistors.

The assembly 10 holds the transistors 12 above the board 24 such thatthe bottom ends of the leads 22 can be passed through lead apertures 28in the board 24 and wave soldered or otherwise electrically connected tothe board. When electricity from a power source 30 or the like is passedthrough the board 24 and through the transistors 12, the transistorsgenerate a substantial amount of heat. The heat sink 18 adjacent to thetransistors 12 draws the heat away from the transistors to the heatsink, and the heat is then dissipated away from the heat sink. As aresult, the assembly 10 acts to support the plurality of transistors 12in positions that, for example, conform to strict manufacturingstandards, and that allow the transistors to be properly installed onthe board by mounting the assembly onto the board 24 as a unit.

As best seen in FIGS. 2 and 3, the transistors 12 are sandwiched betweena forward and rear electric insulators 14 and 16, and the sandwichstructure is clamped against the heat sink 18. The heat sink 18 is avertically oriented plate of aluminum or other thermally conductivematerial, that has alignment bosses 38 that extend forwardly from aforward planar mounting surface 34. The alignment bosses 38 pass throughrespective alignment holes 48 in the rear insulator 16 to position theinsulator 16 in the proper position flush with the mounting surface 34.As best seen in FIG. 3, fastener apertures 40 are foraged in the topportion of the heat sink 18 and receive screws 42 that are threaded intothreaded bosses 78 attached to a support plate 72 of the clamp 20 tofasten the assembly 10 together.

The rear insulator 16 is a plate of thermally conductive plastic orother suitable material that is not electrically conductive. The rearinsulator 16 is shaped and sized to fully cover the mounting surface 34of the heat sink 18, and fastener apertures 44 in the top portion of therear insulator align with the fastener apertures 40 in the heat sink 18.In the preferred embodiment, the bottom portion of the rear insulator 16extends below a bottom edge of the heat sink 18 to prevent the heat sinkfrom coming into contact with the board 24.

The transistors 12 have a backsurface a body 54 with 52 that is pressedagainst the rear insulator 16, and the leads 22 extend downward from thebottom of the transistor body parallel to the rear insulator.Accordingly, the backsurfaces 52 of the transistors 12 only contact therear insulator 16, so they are completely insulated, electrically, fromthe heat sink 18.

The forward insulator 14 is positioned against a front surface 58 of thetransistors 12 and is attached to the rear insulator 16, such that thetransistors 12 are sandwiched between the insulators. In the preferredembodiment, the forward insulator 14 is a contoured, thermallyconductive plastic sheet, or other suitable material that is notelectrically conductive, that has a vertically oriented top portion withfastener apertures 62 therein. The top portions of the forward and rearinsulators 14 and 16 have approximately the same shape and size and arepressed against each other, so the fastener apertures 44 and 62 in theinsulators coaxially align.

The forward insulator 14 is contoured to electrically isolate the tops64 and front surfaces 58 of the transistors 12. A horizontal section ofthe forward insulator 14 located below the top portion, extends over thetops 64 of the transistors 12. The bottom portion of the forwardinsulator 14 extends vertically downward from the horizontal section,covers the front surfaces 58 of the transistors 12, and terminates justbelow the bottom of the transistor bodies 54. Accordingly, thetransistors 12 are surrounded by the insulators 14, 16 on the back 52,top 64, and front surfaces 58, with the bottom being open so the leads22 can extend downwardly in an unobstructed manner from the transistorbodies parallel to the rear insulator 16 and attach to the board.

As best seen in FIG. 3, the clamp 20 has a body portion 70 that connectsto the top of the mounting legs 26. The body portion 70 substantiallyfollows the contour of the forward insulator 14 and has a verticallyoriented support plate 72 that connects to a horizontal section 74,which extends over the tops 64 of the transistors 12. The horizontalsection 74 connects to a plurality of resilient retaining fingers 76that extend downward therefrom and slope rearward toward the transistors12. The retaining fingers 76 exert a retaining force on the transistors12 sandwiched between the insulators 14 and 16 so as to hold thetransistors in the predetermined positions.

The support plate 72 is secured to the top portion of the heat sink 18,so the top portions of the forward and rear insulators are sandwichedbetween the clamp and the heat sink. As mentioned above, the supportplate 72 also has secured thereto threaded bosses 78 that coaxiallyalign with fastener apertures 44 and 62 in the insulators 14 and 16 andwith the fastener apertures 40 in the heat sink 18. Accordingly, theassembly 10 is securely fastened together by the two screws 42, thatextend through the fastener apertures, 44, 62 and 40 and engage thethreaded bases 78.

The clamp 20 of the preferred embodiment has one respective resilientretaining finger 76 for each of the transistors 12. Each of theretaining fingers 76 has a bottom portion that bends and flares forwardaway from the transistor 12, so as to provide a smooth, horizontalengagement portion 82 that presses against the bottom portion of theforward insulator 14. The clamp 20 is a resilient metal, such asstainless steel or the like, that will allow the retaining fingers 76 todeflect slightly when the clamp is fastened to the heat sink 18 andpressed against the forward insulator 14 and transistors 12. Thisdeflection of the retaining fingers 76 exerts the retaining force on thetransistors 12 to support them in a predetermined position with adequatespacing relative to adjacent transistors. Although the preferredembodiment uses stainless steel, other suitable materials can be used.

Each of the two mounting legs 26 of the clamp 20 have a forked bottomportion with two downwardly extending tines 86 that are adapted to beinserted into apertures 88 formed in the printed circuit board 24, asseen in FIG. 2, and to retain the assembly 10 on the board. The tines 86have notches 90 formed therein that receive the board 24 around theapertures 88 to lock the tines 86 in their respective apertures 88 whenthe mounting legs 26 are pushed into engagement with the board. As such,the mounting legs 26 support the assembly 10 substantially perpendicularto the board 24, with the transistors 12 and leads 22 positioned overthe lead apertures 28 in the board. The mounting legs 26 provide supportfor the assembly 10, in part because they are oriented perpendicular tothe support plate 72 so the mounting legs extend in the fore and aftdirection and provide stability to the assembly 10 when it is mountedonto the board 24.

Additional support is provided to the assembly 10 by stabilizingshoulders 92 that are connected to the rear tines 86 of the mountinglegs 26. The stabilizing shoulder 92 is a horizontal member extendingrearwardly from rear tine 86 of each mounting leg 26, that rest on theupper surface of the board when the assembly 10 is installed thereon.Accordingly, the stabilizing shoulder 92 protects against the assembly10 tipping over after being mounted to the board 24, and, thus, theassembly is a self supporting unit mountable on the board. As best seenin FIG. 3, the stabilizing shoulder 92 extends through cut out areas 94and 96 formed in the lower comers of the heat sink 18 and the rearinsulator 16 to avoid interference with the heat sink and rear insulatorwhile maximizing the size and area of the electrically insulated heatsink.

Accordingly, the assembly 10 provides a structure that holds and retainsthe transistors 12 perpendicular to the board 24 with the transistorbodies 54 at predetermined distances above the board and with the leads22 extending downwardly through the lead apertures 28 and connecting tothe board without bending forces being exerted on the leads.

As best seen in FIG. 5, an alternate embodiment of the present inventionhas a heat sink 100 that attaches to the forward and rear electricinsulators 14 and 16, the transistors 12, and the clamp 20 as discussedabove. The alternate heat sink 100 has two horizontally aligned fins 102that are integrally attached to the top portion of the heat sink andextend forwardly over the assembly 10. The fins 102 provide additionalsurface area of the heat sink 100, which improves the performance of theheat sink to allow for greater dissipation of the heat generated fromthe transistors when electricity is passed therethrough. Although theheat sink 100 of the alternate embodiment incorporates two integralfins, a greater or lesser number of fins can be used to achieve adesired heat sink performance. In addition, the fins 102 can beremovable or otherwise not integral to the body of the heat sink 100 to,for example, facilitate manufacturing or the like.

To achieve precise positioning of the transistors, as often is requiredby strict manufacturing standards, a fixture 120, as best seen in FIGS.4 and 5 is used to position the several components of the assembly 10 incorrect positions with proper spacing and orientation, whereby theassembly 10 can be fastened together, removed as a unit, and placeddirectly onto a printed circuit board with all of the components intheir proper positions.

The fixture 120 of the preferred embodiment has a base 122 with a lowerforward section 126 and a raised rearward section 128, wherein the topof the lower section is flat and forms a horizontal datum surface 124representing the top surface of the printed circuit board. The raisedsection 128 is integral with the lower section 126 and extends upwardfrom the datum surface 124 so as to form a vertical back wall 130 thatis perpendicular to the datum surface. The lower section 126 has aplurality of lead apertures 132 formed therein forward of the back wall130 and arranged parallel to the back wall. The lead apertures 132 arepositioned along the datum surface 124 so as to receive the leads 22 ofthe transistors 12. In a preferred embodiment, the lead apertures 132have counter-sunk top portions 134 that facilitate insertion of theleads 22 into the apertures.

As best seen in FIG. 4, slots 136 extend along left and right sides ofthe lower section 126 and terminate at clamp receiving areas 138 formedin the back wall 130. The receiving areas 138 are shaped and sized toreceive the mounting legs 26 of the clamp 20, so the clamp can be movedlaterally through the slots 136 and into an installation position in thereceiving area with the support plate 72 adjacent to the back wall 130.Each of the receiving areas 138 has outer sidewalls 140 that are locatedapart from each other a distance that is slightly greater than thelength of the heat sink 18, so the outer sidewalls form a keyway thatpositions the heat sink on the fixture 120 in a desired position.

A heat sink stop 142 is attached to the datum surface 124 and extendsupward along the back wall 130. The heat sink stop 142 has a flat topsurface 144 that is adapted to support the heat sink 18 at apredetermined position above the datum surface 124. In the preferredembodiment, the heat sink stop 142 is integral with the lower section126 and with the back wall 130 of the raised section 128.

A plate structure 146 having a plurality of support pegs 148 along itsrear portion is fastened to the datum surface 124 between the slots 136.The support pegs 148 are positioned parallel to the back wall and arespaced apart a distance that allows a transistor to span between twoadjacent support pegs and be carried by the support pegs at thepredetermined distance above the datum surface 124.

As best seen in FIGS. 4 and 6, the plate structure 146 has a pluralityof recessed areas 154 between the support pegs 148 that are shaped sothe lead apertures 132 are accessible and so the transistors 12, shownin phantom lines, can be placed onto the support pegs with the leads 22extending downward and into the lead apertures 132. Each of the supportpegs 148 has at least one shoulder portion 156 that receives one side ofa transistor 12 such that a transistor is fully supported by setting onthe shoulder portions of two support pegs. In addition, the shoulderportion 156 of one support peg 148 located on, for example, a left sideof a recessed area 154 is located at the same distance above the datumsurface 124 as the shoulder portion of an adjacent support peg on theright side of the same recessed area. Accordingly, when a transistor 12is positioned onto the shoulder portions 156, the transistor issupported with a predetermined alignment and is positioned at apredetermined distance above the datum surface 124.

In one embodiment of the fixture, the shoulder portions 156 of thesupport pegs 148 are all located at a same distance above the datumsurface 124, because only one type of transistor is used in the assemblythat is assembled in that fixture. In an alternative embodiment of thefixture, the shoulder portions 156 on different sides of a support peg148 are at different distances above the datum surface 124 becauseadjacent transistors 12 in an assembly that is assembled in that fixtureare to be arranged with different clearances over the board. However,the shoulder portions 156 located on opposite sides of a recessed area154 are the same distance above the datum surface 124 so the leads 22 ofthe transistor 12 will be perpendicular to the board 24.

In the preferred embodiment illustrated in FIG. 4, support pegs 148 haverear sidewalls 150 located forward of the heat sink stop 142 so a gap152, as best seen in FIG. 5, is formed between the support pegs 148 andthe heat sink stop. This gap 152 has a thickness slightly greater thanthe thickness of the rear insulator 16. When the heat sink 18 is placedbetween the sidewalls 140 and on the heat sink stop 142, the rearinsulator 16 is installed adjacent to the heat sink with the bottomportion of the rear insulator extending into the gap 152 below thebottom of the heat sink.

In the preferred embodiment, each support peg 148 has a retaining lip158 that engages a transistor body 54 and blocks it from inadvertentlysliding off the forward edge of the support peg. In addition, a block162 is attached to the top of the support peg 148 so as to form achannel 160 between the block and the retaining lip 158. The channels160 are sized to receive the forward insulator 14 and to retain it nextto the transistors 12 on the support pegs 148.

As best seen in FIG. 5, the fixture 120 is used to position and join thecomponents of the assembly 10. After the heat sink 18 is positioned inthe fixture 120 on the heat sink stop 142, and the rear insulator 16 isplaced adjacent the heat sink and in the gap 152, as discussed above, aplurality of transistors 12 are set onto the support pegs 148 so thetransistor bodies 54 are adjacent to the rear insulator 16 and theelectric leads 22 extend into the lead apertures 132. Thereafter, theforward insulator 14 is set onto the support pegs 148 in the channels160 so the transistors 12 are sandwiched between the insulators 14 and16. The clamp 20 is moved into position against the forward insulator 14with the mounting legs 26 passing through the slots 136 of the fixture120. When the clamp 20 is in position, the fasteners 42 are installedand securely fasten the assembly together as a unit so the retainingfingers 76 of the clamp 20 exert the retaining force against thetransistors 12 and hold them in the predetermined position relative tothe datum surface. After the assembly is fastened together, it is raisedout of the fixture 120 as a unit and thereafter installed into theprinted circuit board, as discussed above.

Numerous modifications and variations of the invention disclosed hereinwill occur to those skilled in the art in view of this disclosure. Forexample, the transistors may be replaced with other electroniccomponents having body portions and electric leads that are mountable ina printed circuit board or other similar retaining device. Therefore, itis to be understood that these modifications and variations, andequivalents thereof may be practiced while remaining within the spiritand the scope of the invention as defined by the following claims.

We claim:
 1. A heat sink and transistor retaining assembly that isadapted to be installed onto a printed circuit board coupled to a sourceof electricity, comprising:a heat sink having a bottom edge portionadapted to be disposed adjacent said printed circuit board when saidheat sink projects perpendicularly from a surface of said printedcircuit board, said heat sink having a planar mounting surface and beinga thermally conductive material; a first electric insulator mounted onsaid planar mounting surface of said heat sink said first electricinsulator being thermally conductive; a plurality of transistorspositioned against said first electric insulator, whereby saidtransistors are electrically insulated from said heat sink, each of saidtransistors having electric leads that extend below said bottom edge ofsaid heat sink and that are adapted to engage said printed circuitboard, said transistors generating heat when the electricity is passedtherethrough, whereby said heat passes through said first electricinsulator to said heat sink and dissipates from said heat sink: a secondelectric insulator positioned adjacent said transistors with saidtransistors sandwiched between said first and second electricinsulators; and a resilient clamp attached to said heat sink, said clamphaving a resilient retaining member that exerts a retaining force onsaid transistors through said second electric insulator to retain saidtransistors between said first and second electric insulators inpredetermined positions, whereby said transistors are supported in thepredetermined positions prior to being connected to said printed circuitboard, said resilient retaining member having a respective resilientretaining finger for each of said transistors, said retaining fingersbeing connected to a common support plate that is secured to said heatsink, said retaining fingers exerting said retaining force on saidtransistors.
 2. The heat sink and transistor assembly of claim 1 whereinat least one of said clamp and heat sink has means for mounting saidassembly onto said printed circuit board.
 3. The heat sink andtransistor retaining assembly of claim 1 wherein each of saidtransistors is supported in a selected one of the predeterminedpositions, the predetermined positions being at a same distance abovethe bottom edge of the heat sink.
 4. The heat sink and transistorretaining assembly of claim 1 wherein each of said transistors issupported in a selected one of the predetermined positions, thepredetermined positions being more than one distance above the bottomedge of the heat sink.
 5. The heat sink and transistor retainingassembly of claim 1 wherein said heat sink has at least one fin.
 6. Theheat sink and transistor retaining assembly of claim 1 wherein said heatsink is aluminum.
 7. The heat sink and transistor retaining assembly ofclaim 1 wherein said first and second electric insulators are plastic.8. The heat sink and transistor retaining assembly of claim 1, furthercomprising alignment means connected to said heat sink and adapted toalign said first electric insulator against said base plate.
 9. Aprinted circuit board assembly comprising:a printed circuit board havinga plurality of lead apertures and at least one retaining aperture saidprinted circuit board being adapted to connect to a source ofelectricity: a heat sink having a bottom edge portion adapted to bedisposed adjacent said printed circuit board when said heat sinkprojects perpendicularly from a surface of said printed circuit board,said heat sink having a planar mounting surface and being a thermallyconductive material; a first electric insulator mounted on said planarmounting surface of said heat sink, said first electric insulator beingthermally conductive; a plurality of transistors positioned against saidfirst electric insulator, whereby said transistors are electricallyinsulated from said heat sink, each of said transistors having electricleads that extend below said bottom edge of said heat sink and throughsaid lead apertures in said printed circuit board, said transistorsgenerating heat when the electricity is passed therethrough, wherebysaid heat passes through said first electric insulator to said heat sinkand dissipates from said heat sink: a second electric insulatorpositioned adjacent said transistors with said transistors sandwichedbetween said first and second electric insulators; and a resilient clampattached to said heat sink, said clamp having a resilient retainingmember that exerts a retaining force on said transistors through saidsecond electric insulator to retain said transistors between said firstand second electric insulators in predetermined positions, whereby saidtransistors are supported in the predetermined positions prior to beingconnected to said printed circuit board, said resilient retaining memberhaving a respective resilient retaining finger for each of saidtransistors, said retaining fingers being connected to a common supportplate that is secured to said heat sink, said retaining fingers exertingsaid retaining force on said transistors.
 10. The printed circuit boardassembly of claim 9 wherein at least one of said clamp and heat sink hasmeans engaging said printed circuit board at said at least one retainingaperture for mounting said assembly onto said printed circuit board. 11.The printed circuit board assembly of claim 9 wherein each of saidtransistors is supported in a selected one of the predeterminedpositions, the predetermined positions being at a stone distance abovethe bottom edge of the heat sink.
 12. The printed circuit board assemblyof claim 9 wherein each of said transistors is supported in a selectedone of the predetermined positions, the predetermined positions beingmore than one distance above the bottom edge of the heat sink.
 13. Theprinted circuit board assembly of claim 9 wherein said heat sink has atleast one fin.
 14. The printed circuit board assembly of claim 9 whereinsaid heat sink is aluminum.
 15. The printed circuit board assembly ofclaim 9 wherein said first and second electric insulators are plastic.16. The printed circuit board assembly of claim 9, further comprisingalignment means connected to said heat sink and adapted to align saidfirst electric insulator against said heat sink.
 17. A heat sink andtransistor retaining assembly that is adapted to be installed onto aprinted circuit board coupled to a source of electricity, comprising:aheat sink having a bottom edge portion adapted to be disposed adjacentsaid printed circuit board when said heat sink projects perpendicularlyfrom a surface of said printed circuit board said heat sink having aplanar mounting surface and being a thermally conductive material; afirst electric insulator mounted on said planar mounting surface of saidheat sink, said first electric insulator being thermally conductive; aplurality of transistors positioned against said first electricinsulator, whereby said transistors are electrically insulated from saidheat sink, each of said transistors having electric leads that extendbelow said bottom edge of said heat sink and that are adapted to engagesaid printed circuit board said transistors generating heat when theelectricity is passed therethrough, whereby said heat passes throughsaid first electric insulator to said heat sink and dissipates from saidheat sink; a second electric insulator positioned adjacent saidtransistors with said transistors sandwiched between said first andsecond electric insulators; a resilient clamp attached to said heatsink, said clamp having a resilient retaining member that exerts aretaining force on said transistors through said second electricinsulator to retain said transistors between said first and secondelectric insulators in predetermined positions, whereby said transistorsare supported in the predetermined positions prior to being connected tosaid printed circuit board; and alignment means connected to said heatsink and adapted to align said first electric insulator against saidbase plate.
 18. The heat sink and transistor assembly of claim 17wherein at least one of said clamp and heat sink has means for mountingsaid assembly onto said printed circuit board.
 19. The heat sink andtransistor retaining assembly of claim 17 wherein each of saidtransistors is supported in a selected one of the predeterminedpositions, the predetermined positions being at a same distance abovethe bottom edge of the heat sink.
 20. The heat sink and transistorretaining assembly of claim 17 wherein each of said transistors issupported in a selected one of the predetermined positions, thepredetermined positions being more than one distance above the bottomedge of the heat sink.
 21. The heat sink and transistor retainingassembly of claim 17 wherein said heat sink has at least one fin.